Method and apparatus for control of high voltage corona discharge in electrostatic dust separators



Jan. 1970 HORST GUNTER EISHOLD 3,488,?5

METHOD AND APPARATUS FOR CONTROL OF HIGH VOLTAGE CORONA DISCHARGE" IN ELECTROSTATIC DUST SEPARATORS Filed April 5, 1966 2 Sheets-Sheet 1 Fig.1

In venfur:

yams rads rm E/SHOLD 1970 HORSTGUNTER EISHOLD 3, METHOD AND APPARATUS FOR CONTROL OF HIGH VOLTAGE CORONA DISCHARGE IN ELECTROSTATIC DUST SEPARATORS Filed April 5, 1966 2 Sheets-Sheet 2 III g S ,arraR 5 United States Patent Oflice 3,488,675 Patented Jan. 6, 1970 3,488,675 METHOD AND APPARATUS FOR CONTROL OF HIGH VOLTAGE CORONA DISCHARGE IN ELECTROSTATIC DUST SEPARATORS Horst-Gunter Eishold, Frankfurt am Main, Germany, assignor to Metallgeselischaft Aktiengesellschaft, Frankfurt am Main, Germany Filed Apr. 5, 1966, Ser. No. 540,371 Claims priority, application Germany, Apr. 10, 1965, M 64,844 Int. Cl. B03c 3/68, 3/02 U.S. Cl. 55-2 Claims ABSTRACT OF THE DISCLOSURE A device for generating a control signal which represents the intensity and frequency of corona discharges of an electrostatic separator having electrodes for inducing corona discharges and synchronizing the induced corona discharges for an optimum rate.

This invention relates in general to electrostatic precipitators including electrostatic dust separators, and more particularly to a method and apparatus for effecting control of high voltage corona discharges occurring in electrostatic dust separators.

In general, controls for the regulation of high voltages applied to the emitter and collector electrodes of electrostatic dust separators wherein the potential difference between such electrodes is set so high that corona discharges constantly occur, are known in the prior art. In these cases, the dust separation performance first increases with the number of corona discharges per unit of time, and then drops off after passing through an optimum corona discharge rate. Experience indicates that the optimum corona discharge rates are about 150 discharges per minute. For best performance, the control means which governs the voltage applied to the electrodes must therefore be so operated that this optimum discharge repetition frequency is constantly maintained. To do this, it is essentially necessary to count the number of corona discharges actually occurring over a reference time interval, which is preferably done electrically by sensing variations in the currents which occur as a result of the corona discharges. In the prior art, these current variations, which are pulselike, are usually detected on the secondary side of the high voltage transformer which energizes the electrodes.

Control systems are also known in which the current pulse detection or sampling of the current pulses is performed on the primary side of the high voltage transformer. In such systems, the pulse detection or pickup is performed galvanically in one of three different methods. The first method is commonly designated as the ohmic detection or ohmic pickup of the pulses, and is described, for example in the German printed applications 1,148,977 and 1,179,541. Another pulse detection method is the inductive method which is described in US. Patent 2,297,740. A further method that is widely used, as is the inductive pickup method, is the capacitative pulse detection method which can be performed on the high voltage side of the transformer as described, for example in US. Patent 2,623,608.

Usually, the current pulses detected by such methods are amplified and transformed or otherwise modified in wave shape, so as to have current and voltage values dependent upon the number of discharges per unit time. Essentially, the wave shape of such detected pulses corresponds to the intensity and frequency of the corona discharges occurring in the separator, and hence can be utilized to control a circuit which regulates the high voltage applied to the electrodes.

In accordance with the latest state of development in the electronics art, such regulating circuits and their associated amplifiers and pulse transformers are usually transistorized. As is well known to the artisan, corona discharges inherently generate high frequency current and voltage components extending well into the radio frequency range, and in fact, before the advent of the electron tube, were used for the generation of radio frequency electromagnetic energy used for radio communication. Consequently, difficulties have always occurred hitherto in utilizing the aforementioned methods of sensing the currents or voltages resulting from corona discharges because of their high frequency components which tend to overload and damage the electronic components of the sensing equipment and signal processing equipment coupled thereto. Particularly in the case of transistorized equipment, there is an urgent need for isolating such high frequency components from any transistors used in the detecting circuitry, since transistors are extremely sensitive to overloading.

According to the invention, the danger of overloading, particularly voltage overloading is eliminated by the use of an optical coupling circuit.

The invention proposes a method for controlling the high voltage of electrostatic dust separators according to the number and/or the intensity of the electrical discharges occurring therein as indicated by the current or voltage pulses resulting from such discharges, with the transmission of such pulses from the voltage supply circuit of the dust separator to the controlling device taking place optically by luminous signals.

According to a further development of the invention, the variations in brightness in a glow-discharge or incandescent lamp responding to the electrical discharges in the electrostatic dust separator are detected by a photoelectric cell inserted into the control circuit and are transformed in a prior art manner into electrical control impulses.

According to the invention, the glow-discharge or incandescent lamp can be connected in parallel with an electrical resistance in the high voltage supply circuit. The relatively brief current changes of the corona discharges produce variations in the brightness of the lamp, which variations are detected by the photoelectric cell which can be of any conventional type such as a selenium cell or a cadmium sulfide cell, silicon cell, etc. The photo electric cell serves to generate an electrical signal the voltage and current of which corresponds to the illumination intensity of the lamp andthus has a wave shape representative of the frequency and intensity of the corona discharges sensed by the lamp. Hence, the photoelectric cell actually generates a signal which after suitable amplification such as by a transistorized preamplifier, can be used to control the operation of a circuit which supplies high voltage to the dust separator electrodes,

Essentially, the invention provides a method for generating a control signal representing the intensity and frequency of corona discharges repeatedly occurring in an electrostatic dust separator. In this method, a portion of the electrical current resulting from each corona discharge is passed through a lamp, either an incandescent or a glow-discharge lamp to illuminate same with an intensity varying in accordance with the frequency and intensity of such corona discharges. The illumination intensity of the lamp is sensed by a photoelectric cell, which can be either of the photovoltaic or photoconductive type, which generates an electrical signal corresponding to the lamp intensity and hence has a wave shape representing the frequency and intensity of the corona discharges which produced such varying lamp intensity.

In general, the level of the control signal generated by the photoelectric cell will be relatively low, and thus for practical purposes such signal is amplified and then ordinarily applied to a signal comparator which compares it with a reference signal representing a selected corona discharge repetitio-n frequency to derive a second control signal, or error signal representing the deviation from said selected frequency of the repetition frequency of corona discharges actually occurring in the separator.

One of the advantages of the invention lies in the fact that by converting the sensed corona discharge current impulses into light which varies correspondingly in intensity, and then by activating a photoelectric cell with such light optically transmitted thereto, there is no direct electrical signal path from the separator to the photocell and such signal processing equipments as it may be connected to. This effectively precludes any significant coupling of the high frequency corona discharge components into the photocell and associated signal processing equipment, which now can be safely transistorized since the danger of high frequency component overloading is eliminated.

Insofar as their electrical signal outputs are concerned, photoelectric cells have inherent overload protection because above their saturation illumination intensity levels, further increases in incident illumination intensity result in no further increase in signal output.

It is therefore an object of the invention to provide a method for generating a control signal representing the intensity and frequency of corona discharges repeatedly occurring in an electrostatic dust separator.

Another object of the invention is to provide an apparatus for performing the aforesaid method.

A further object of the invention is to provide a method and apparatus as aforesaid whereby the control signal generated is substantially free from high frequency components resulting from such corona discharges.

A further object of the invention is to provide an apparatus as aforesaid including means for amplifying the control signal generated and converting the original wave form thereof into a wave form appropriate for use by a high voltage controller which regulates the high voltage supplied to the dust separator electrodes.

Still another and further object of the invention is to provide an apparatus as aforesaid including signal processing means for converting the control signal generated into a corresponding square-wave pulsed signal.

Other and further objects and advantages of the invention will become apparent from the following detailed description and accompanying drawings in which:

FIG. 1 is a schematic illustration of an apparatus according to a preferred embodiment of the invention for sensing corona discharges in an electrostatic dust separator, and generating a signal characteristically representative of such corona discharges for use in controlling the high voltage applied to electrodes within the separator that produce such discharges.

FIG. 2 is a schematic illustration of an apparatus according to another embodiment of the invention for generating a similar corona discharge signal, and including means for amplifying and modifying the wave shape of such signal.

Referring now to the drawings, the schematically rep resented electrostatic dust separator 1 has a set of emitter electrodes 2 and collector electrodes 3. The emitter and collector electrodes 2 and 3 are connected to a high voltage source (not shown) which repeatedly establishes a high potential difference between them to induce corona discharges between said electrodes 2 and 3. The emitter or corona electrodes 2 are connected through a conductor line 4 tothe high voltage source and the collector or precipitation electrodes 3 are connected through another conductor line 5 to the ground reference terminal of the high voltage source.

In the embodiment of the invention illustrated by FIG. 1, a variable resistor 6 is connected in series into the ground lead 5, and in parallel with an incandescent or glow-discharge lamp 7. A portion of the electrical current resulting from corona discharges between the electrodes 2 and 3 and passing from the electrode 3 to resistor 6, will be diverted to the lamp 7 and will illurninate same with a brightness which varies in accordance with the corona discharge currents in the electrostatic dust separator 1. These brightness variations are picked up by a photoelectric cell 8, amplified by a transistor 9 and fed to a signal processing circuit means 10, such as an impulse transformer or an integrator circuit.

The signal processor 10 receives its supply voltages for operation through terminal connectors 11 and delivers its output signal at an output line 12. At the output 12, a number of signal impulses corresponding to the number of corona discharge current variations is picked up and delivered in a conventional manner to a controlling apparatus (not shown) for controlling the high voltage applied to the electrodes 2 and 3. For the sake of simplicity, the signal processor 10 has been shown only in block form, since impulse transformers and integrator stages are sufficiently well known to those skilled in the art. Such devices are illustrated, for example, in the previously mentioned patents, as are examples of high voltage controlling apparatus.

In FIG. 1, the lamp 7 is connected in a series-parallel arrangement with the electrodes 2 and 3 of the dust separator 1, so that corona discharge currents flowing from the emitter electrode 2 are received by the collector electrode 3 which is connected in series with the parallel combination of the resistor 6 and lamp '7, so that a portion of the corona discharge current flowing through the dust separator 1 is returned to ground through the lamp 7. The embodiment represented by FIG. 2 differs from that in FIG. 1 in that the lamp 7 is connected in parallel with the electrostatic dust separator 1. The voltage for the operation of the lamp 7 is obtained across the parallel resistors 6 and 6 which are in turn connected in series with another resistor 16 that is connected to the emitter electrode 2. To provide an adjustment capability in setting the reference level of lamp 7 brilliance, the resistor 6 is preferably a variable resistor 6. Here again, the brightness variations of the lamp 7 are detected by a photoelectric cell 8 and fed to an amplifying transistor 9.

The amplified output of transistor 9 is fed to the input of a signal processor 10, which is illustrated as a Schmitt trigger circuit in FIG. 2. The Schmitt trigger circuit 10 is operated by the signal voltage variations of the photoelectric cell 8, which are amplified by the transistor 9. At the output 12 of the Schmitt trigger 10', there appears a number of square-wave impulses corresponding to the number of current variations. These impulses can be further processed by a conventional high voltage controller (not shown).

As to the choice between using either an incandescent lamp 7 or a glow-discharge lamp 7, measurements with the aforementioned apparatus circuits have shown that if thin filament type incandescent lamp 7 are used, impulse frequencies of more than cycles per second can be transmitted optically by such incandescent lamp 7 to the photo cell 8. However, glow-discharge lamps 7 offer the advantage of having relatively little thermal inertia as compared with incandescent lamps 7, so that with glowdischarge lamps 7 a somewhat more faithful luminous reproduction of corona discharge current pulses can be transmitted.

The invention offers a decided advantage in the controlling of the high voltage applied to the electrodes of electrostatic dust separators 1, since the actual corona discharge performance can be sensed in a manner whereby there is no direct electrical contact between any high voltage carrying parts of the separator and the controlling or regulating apparatus. Furthermore, with the electrooptical signal transmission provided by the invention, overload damage to transistorized components as the result of high frequency components produced by corona discharges, is eliminated.

From the foregoing, it can be appreciated that the invention provides an apparatus for generating an electrical control signal at the output of a photocell 8, having a wave form representing the intensity and frequency of corona discharges repeatedly occurring between the emitter and collector electrodes 2 and 3 when supplied by a high voltage source which repeatedly establishes a potential difference between said electrodes 2 and 3 sufiiciently high to induce such corona discharges. This apparatus has circuit means including one or more electrical resistors, 6, 6, 16, connected to one of the electrodes 2, 3 and to the ground reference terminal of the high voltage source for receiving electrical current resulting from each corona discharge, and diverting a portion of said current to a lamp 7 coupled to said circuit means. In FIG. 1, such circuit means is defined by the combination of the resistor 6 and conductor line 5. Resistor 6 is connected in FIG. 1 to the collector electrode 3, and to the ground terminal and is also connected to the lamp 7 to divert a portion of the current from electrode 3 to said lamp 7 for illumination thereby. In FIG. 2, this circuit means corresponds to the network defined by the resistors 16, 6 and 6. This network is connected to the emitter electrode 2 through the series resistor 16 and to the lamp 7 at the parallel connection of resistor 6 and 6'.

What is claimed is:

1. A method for generating a control signal representing the intensity and frequency of corona discharges repeatedly occurring in an electrostatic dust separator, which comprises passing a portion of the electrical current resulting from each corona discharge through a lamp to illuminate same with an intensity varying in accordance with the frequency and intensity of such corona discharges, and sensing the illumination intensity of said lamp by a photoelectric cell to generate thereby a corresponding electrical signal representing the frequency and intensity of said corona discharges.

2. The method according to claim 1 including the steps of amplifying the control signal generated by the photoelectric cell, and applying said amplified control signal to a signal comparator for comparing said control signal with a reference signal representing a selected corona discharge repetition frequency to derive a second control signal representing the deviation of the repetition frequency of corona discharges occurring in said separator from said selected frequency.

3. The method according to claim 1 including the steps of amplifying the control signal generated by the photoelectric cell, and converting the Wave form of said amplified control signal into a corresponding train of squarewave pulses.

4. An apparatus for generating a control signal representing the intensity and frequency of corona discharges repeatedly occurring between emitter and collector electrodes in an electrostatic dust separator wherein said electrodes are connected to a high voltage source which repeatedly establishes a high potential difference therebetween for inducing such corona discharges, which comprises circuit means including an electrical resistance, connected to one of said electrodes and to a reference terminal of said high voltage source for receiving a varying electrical current resulting from each corona discharge and diverting a portion of said current, a lamp coupled to said circuit means to receive the portion of electrical current diverted thereby for illumination with an intensity varying in accordance with the frequency and intensity of said corona discharges, and a photoelectric cell disposed to sense the illumination intensity of said lamp to generate a corresponding electrical signal having a wave shape thus representing the frequency and intensity of said corona discharges.

5. The apparatus according to claim 4 wherein the circuit means includes a resistor connected to the collector electrode of said separator and to the reference terminal of the high voltage source, and wherein said lamp is connected in shunt to said resistor.

6. The apparatus according to claim 4 wherein said circuit means includes an electrical resistance network connected to the emitter electrode of said separator and to the reference terminal of the high voltage source,

7. The apparatus according to claim 4 wherein said lamp is an incandescent lamp.

8. The apparatus according to claim 4 wherein said lamp is a glow-discharge lamp.

9. The apparatus according to claim 4 including an amplifier coupled to said photoelectric cell to amplify the signal generated thereby, and a fixed time period trigger circuit coupled to said amplifier to convert the wave form of the control signal amplified thereby into a corresponding train of square-wave pulses.

10. The apparatus according to claim 4 including an amplifier coupled to said photoelectric cell to amplify the signal generated thereby, and an integrator circuit means coupled to said amplifier to convert the wave form of the control signal amplified thereby into a signal having a wave form representing the time interval of said control signal.

References Cited UNITED STATES PATENTS 2,189,614 2/1940 Penney 55-105 2,297,740 10/1942 Brown 55105 X 2,623,608 12/1952 Hall 55-105 2,632,522 3/1953 Fields 5510'4 2,742,104 4/1956 Hall 55-104 2,771,150 11/1956 Welts 55-105 2,783,388 2/1957 Wintermute 55105 X 2,935,155 5/1960 Foley 55-105 2,943,697 7/1960 Little 55-10'5 2,961,577 11/1960 Thomas et a1. 5510 5 2,979,158 4/1961 Vlier 55139 3,114,097 12/1963 Clarke 321-18 3,173,772 3/1965 Gelfand.

FOREIGN PATENTS 65,045 11/ 1946 Denmark.

1,130,971 10/1956 France.

488,943 1/1930 Germany.

701,855 1/1954 Great Britain.

705,604 3/ 1954 Great Britain.

520,183 3/1955 Italy.

OTHER REFERENCES German printed application, No. 1,148,977, May 1963. German printed application, No. 1,179,541, October 1964.

HARRY B. THORNTON, Primary Examiner DENNIS E. TALBERT, In, Assistant Examiner US. Cl. X.R. 55105, 139 

